clutter-offscreen-effect: Don't redraw the actor if cached offscreen

When painting an actor, it now tries to determine if the last paint of
the offscreen was using the same matrix and the actor isn't dirty. If
so, it can skip calling clutter_actor_continue_paint and avoid
actually painting the actor. Instead just the offscreen image will be
painted.

clutter/clutter-offscreen-effect.c

@@ -89,6 +89,16 @@ struct _ClutterOffscreenEffectPrivate
   gfloat target_height;
 
   gint old_opacity_override;
+
+  /* The matrix that was current the last time the fbo was updated. We
+     need to keep track of this to detect when we can reuse the
+     contents of the fbo without redrawing the actor. We need the
+     actual matrix rather than just detecting queued redraws on the
+     actor because any change in the parent hierarchy (even just a
+     translation) could cause the actor to look completely different
+     and it won't cause a redraw to be queued on the parent's
+     children. */
+  CoglMatrix last_matrix_drawn;
 };
 
 G_DEFINE_ABSTRACT_TYPE (ClutterOffscreenEffect,
@@ -244,6 +254,11 @@ clutter_offscreen_effect_pre_paint (ClutterEffect *effect)
    */
   cogl_get_modelview_matrix (&modelview);
 
+  /* Store the matrix that was last used when we updated the FBO so
+     that we can detect when we don't need to update the FBO to paint
+     a second time */
+  priv->last_matrix_drawn = modelview;
+
   /* let's draw offscreen */
   cogl_push_framebuffer (priv->offscreen);
 
@@ -347,20 +362,11 @@ clutter_offscreen_effect_real_paint_target (ClutterOffscreenEffect *effect)
 }
 
 static void
-clutter_offscreen_effect_post_paint (ClutterEffect *effect)
+clutter_offscreen_effect_paint_texture (ClutterOffscreenEffect *effect)
 {
-  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (effect);
+  ClutterOffscreenEffectPrivate *priv = effect->priv;
-  ClutterOffscreenEffectPrivate *priv = self->priv;
   CoglMatrix modelview;
 
-  if (priv->offscreen == COGL_INVALID_HANDLE ||
-      priv->target == COGL_INVALID_HANDLE ||
-      priv->actor == NULL)
-    return;
-
-  cogl_pop_matrix ();
-  cogl_pop_framebuffer ();
-
   cogl_push_matrix ();
 
   /* Now reset the modelview to put us in stage coordinates so
@@ -372,17 +378,60 @@ clutter_offscreen_effect_post_paint (ClutterEffect *effect)
   cogl_matrix_translate (&modelview, priv->x_offset, priv->y_offset, 0.0f);
   cogl_set_modelview_matrix (&modelview);
 
-  /* Restore the previous opacity override */
-  _clutter_actor_set_opacity_override (priv->actor, priv->old_opacity_override);
-
   /* paint the target material; this is virtualized for
    * sub-classes that require special hand-holding
    */
-  clutter_offscreen_effect_paint_target (self);
+  clutter_offscreen_effect_paint_target (effect);
 
   cogl_pop_matrix ();
 }
 
+static void
+clutter_offscreen_effect_post_paint (ClutterEffect *effect)
+{
+  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (effect);
+  ClutterOffscreenEffectPrivate *priv = self->priv;
+
+  if (priv->offscreen == COGL_INVALID_HANDLE ||
+      priv->target == COGL_INVALID_HANDLE ||
+      priv->actor == NULL)
+    return;
+
+  /* Restore the previous opacity override */
+  _clutter_actor_set_opacity_override (priv->actor, priv->old_opacity_override);
+
+  cogl_pop_matrix ();
+  cogl_pop_framebuffer ();
+
+  clutter_offscreen_effect_paint_texture (self);
+}
+
+static void
+clutter_offscreen_effect_run (ClutterEffect         *effect,
+                              ClutterEffectRunFlags  flags)
+{
+  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (effect);
+  ClutterOffscreenEffectPrivate *priv = self->priv;
+  CoglMatrix matrix;
+
+  cogl_get_modelview_matrix (&matrix);
+
+  /* If we've already got a cached image for the same matrix and the
+     actor hasn't been redrawn then we can just use the cached image
+     in the fbo */
+  if (priv->offscreen == NULL ||
+      (flags & CLUTTER_EFFECT_RUN_ACTOR_DIRTY) ||
+      !cogl_matrix_equal (&matrix, &priv->last_matrix_drawn))
+    {
+      /* Chain up to the parent run method which will call the pre and
+         post paint functions to update the image */
+      CLUTTER_EFFECT_CLASS (clutter_offscreen_effect_parent_class)->
+        run (effect, flags);
+    }
+  else
+    clutter_offscreen_effect_paint_texture (self);
+}
+
 static void
 clutter_offscreen_effect_finalize (GObject *gobject)
 {
@@ -414,6 +463,7 @@ clutter_offscreen_effect_class_init (ClutterOffscreenEffectClass *klass)
 
   effect_class->pre_paint = clutter_offscreen_effect_pre_paint;
   effect_class->post_paint = clutter_offscreen_effect_post_paint;
+  effect_class->run = clutter_offscreen_effect_run;
 
   gobject_class->finalize = clutter_offscreen_effect_finalize;
 }